Will macros work with expressions?

[Robert Fraser]

Reiner Pope Wrote:

> Bill Baxter wrote:
> > Xinok wrote:
> >> Bill Baxter wrote:
> >>> A question about the upcoming macros:
> >>> Will they work for expressions as well as statements?
> >>>
> >>> The examples in WalterAndrei.pdf all show complete statements,
> >>> like
> >>>    macro foo(e) { e=3; }
> >>>
> >>> But will it be possible to have:
> >>>    macro foo(e) { e+3 }
> >>>
> >>> I hope expressions will be allowed.  Not for things like e+3 but for 
> >>> making local shortcuts where aliases don't cut it:
> >>>
> >>>    macro call_func( arg ) {
> >>>       $this.some_member.a_really_long_named_template_member(arg);
> >>>    }
> >>>    ...
> >>>    writefln(call_func(1));
> >>>    writefln(call_func("hi"));
> >>>
> >>> And I'm sure there'd be any number of other uses for expression macros.
> >>>
> > 
> >  > I agree that macro expressions should be allowed. However, I think a
> >  > better syntax would be:
> >  >
> >  > macro foo(e) = e + 3;
> >  >
> > 
> > I like that. But what about an expression with a few preliminary 
> > statements setting up temp variables and such?
> > 
> > --bb
> 
> If it's going to be "pasted" into the call-site, then how can that work? 
> I imagine you'd have to set it up as a function call.
> 
> Of course, a nicer solution is a syntax where (nearly) everything is an 
> expression, like many functional languages.
> 
>     -- Reiner

Walter discussed this during his talk I believe. Indeed, macros will do syntax-tree substitution and variable declarations are becoming expressions, so you'll be able to insert temporary variables, etc.

My worry is that macros used inside expressions will not be able to contain statements. This is a shame, since this means that macros and function calls won't be interchangeable. Looks like macros will be slightly more powerful than their C counterparts, which I've never used.